The Butterfly Effect
by minniequill
Summary: "Nobody is supposed to meddle with time! Nobody!" He didn't stop to think of the consequences. He didn't stop to think of the 'what ifs.' AU. Time-travel. Harry takes himself back 50 years to Tom Riddle's adolescence. He won't let the Dark Lord rise again.
1. Chapter 1

**The Butterfly Effect**

 **Author's notes:** So, a time-travel fic. It will no doubt be a touch confusing but I hope you enjoy it nonetheless. I should be working on 'An Unexpected Alliance' but this one seemed to spring to mind almost fully-formed from this line:

"' _NO_!' The scream was the more terrible because he had never expected or dreamed that Professor McGonagall could make such a sound." – DH36

Anyway, I hope you enjoy! Please review.

 **Disclaimer:** I do not own Harry Potter.

 **Summary:** " _Nobody is supposed to meddle with time! Nobody!"_ He didn't stop to think of the consequences. He didn't stop to think of the 'what ifs.'

* * *

 _It has been said that something as small as the flutter of a butterfly's wing can ultimately cause a typhoon halfway across the world._

 _Chaos Theory_

* * *

 **1.**

Harry didn't stop to think of the consequences. He didn't stop to think of the 'what ifs?' He simply took the vial of potion that Hermione made all-those-years ago, and swallowed it in one go. It burned his throat as it went down but he didn't care as he leaned his hands against the oak desk and hung his head.

A dull _thrum_ rang in his ears and a burn pulsed through his veins, so searing hot that he was sure he would ignite at any second. He looked up and caught sight of his reflection in the window. An incandescent glow danced beneath his skin and the room brightened around him. His body emitted light from the inside-out, growing ever-more-brilliant, until it burst from his fingertips. Every corner of the room, every crack in the walls, every cornice in the woodwork was illuminated.

Then; in a burst of dazzling, white flames; he vanished.

-o-

"I thought I might find you here."

Minerva didn't turn at the sound of her sister's voice, just continued to stare at her reflection. She could have sworn, just a second ago, that someone entirely different had been staring back. An older woman, in robes of emerald green, peering over-top square spectacles.

It was unnerving.

"Minerva? I need to ask you a favour," Frances continued.

"Which is?" Minerva asked.

She turned away from the mirror and leaned against the vanity, eyebrows raised.

"There's a man who has just come in. We've never seen wounds like it and… well, none of us can just stand around waiting for him to come to. With Grindlewald sending people in every thirty seconds…" Her voice trailed off and she bit her bottom lip.

"And…?" Minerva pressed gently.

"We'll be busy. Can you just check on him every hour or so?"

Frances looked far too tired, Minerva thought, and it would no doubt be killing her to ask for any form of help.

"Of course," she answered. "Every hour or so."

-o-

 **2.**

"What on earth do you think has happened to him?"

"I'm not sure, maybe…"

Harry opened his eyes to find the dark, blurry forms of a man and woman at the foot of his bed. He winced as he tried to sit upright, and put a hand to his stomach as nausea threatened to overwhelm him. His head pounded, his body felt bruised, beaten and burned like he had been sucked into a fiery abyss and spat out the other side. The bile he fought to push down continued to rise in his throat and he fought hard not to retch. The man flicked his wand and a sphere of light hovered above the bed, casting a soft glow in the room.

The woman conjured a bowl and handed it over as his body heaved again. "Here."

Harry didn't have time to thank her as he vomited up the meagre contents of his stomach. Thankfully, she didn't seem to take offence and waited patiently as he continued to heave until he couldn't bring anything else up. She took the bowl from him after he had finished and vanished it with a casual wave of her wand.

"Do you know where you are?" she asked gently.

Harry glanced around the room, wanting to answer _'yes'_ , but nothing about this room was familiar. Carefully ordered potions housed behind glass lined one wall, books another, and he could see the brightly-lit hallway outside through the large inner window. There looked to be a screen separating the room. It was almost like a…

"The hospital?" he ventured.

The woman gave him a small smile. "Nearly," she said. "You're in Saint Mungos. You were found unconscious in the street a few days ago." She frowned as she looked him up-and-down, taking note of the bruises and burns on his skin. "You've certainly been in strife."

 _You don't know the half of it_.

Harry opened his mouth to respond but there was a mad commotion that caught everybody's attention.

"Montgomery!" a frantic voice shrieked. "Frances!"

The woman looked towards the hallway and Harry's mouth fell open as a man was brought into the outside room. He gushed blood from innumerable wounds, staining the bedsheets crimson, and Harry wasn't surprised when both Healers left the room in a whirl of robes. They were at the man's side in seconds, casting healing spells, and summoned blood-replenishing potions that they tipped down the man's throat.

Harry looked away. It was all too familiar for him, too much like the battles with Voldemort, where he had seen more than one soldier with similar wounds. He sank into the pillow behind him and closed his eyes, wondering where or rather _when_ the hell he had landed. Harry let his body relax, focused on his breathing, and had nearly fallen asleep when a voice spoke.

"Good to see you're with us."

His eyes snapped open and a girl, no more than sixteen-or-so, looked back. She leaned against the doorframe, one ankle crossed over the other, arms folded. She exuded confidence, in herself and her abilities, and dangerously toed the line between that and arrogance.

She reminded him of Hermione.

Her gaze softened, and she crossed to his side to pick up his glasses which rested on the bedside table. "Perhaps you'll feel better with these," she said, handing them to Harry. He immediately slipped them onto his nose, breathing a relieved sigh as the world slid into sharp focus.

"Thank you."

The girl said nothing, just nodded. Harry could see clearly that she was far too young to be a qualified Healer, which begged the question: _'what was she doing here?_ '

"You met my sister, Healer Frances, earlier," she said, answering his unspoken query. "She asked me to keep an eye on you."

"And why are _you_ here?"

The girl's jaw tightened and her eyes narrowed. "My brother, Robert, was injured in the battle before last. I've been allowed time from school to see him."

Harry flushed and offered an apologetic smile that she didn't return. "I'm sorry," he said. "That was rude."

She stayed silent, and Harry swallowed, finding his mouth dry. He opened his mouth to ask for a drink of any kind but the girl conjured a jug of water and glass before he uttered a word and poured him a glass.

"Here."

He drank quickly, finished the glass in seconds, and she immediately poured him another.

"Thank you," he said, another glass later. "What year is it?" Harry asked eventually. A huge part of him dreaded the answer.

She raised an eyebrow. "1942."

The last thing he remembered was the girl's face, and her voice as she screamed for _'Frances,'_ before blackness enveloped him and he fell into nothingness.

-o-

 _She grabbed Robert's hand, holding it as tight as she could, and felt a sob of relief threaten to explode from her mouth when he gave a gentle squeeze back. Tears streamed down her cheeks, and she rocked back-and-forth, never once letting her hold lessen. His grip slackened and she rose to her feet and leaned over him. "No! Don't!" The words slid into each other, until they were a stream of utter nonsense. She squeezed his hand again, trying to bring him back._

 _The scene changed._

" _Come along, Potter," she whispered, holding a boy's hand tightly. She tugged him down a hallway that she recognised from Hogwarts. "Come along… hospital wing." The boy's face was hidden by shadows, and she couldn't make out even his eyes. Nonetheless, she knew he was important and that he needed to be protected. She could certainly do that. She vaguely heard another voice, but paid them no attention, just kept the boy close._

" _He's been through enough, tonight."_

 _The boy squeezed her hand._

Minerva woke with a start in Saint Mungos, next to Robert's bed. He looked no different than he had when she'd fallen asleep. She glanced around the room, searching for any sign of the elusive boy from her dream, but could see no one or nothing important. Minerva yawned and leaned forward again, dismissing the dream as just that. A dream. She rested her head against her folded arms; it wasn't particularly comfortable, propped against a bed, but she had no wish to move any time soon.

Soon enough, her eyes grew heavy, and she slipped back to sleep.

-o-

 **3.**

When Harry woke again, his room was empty. The girl had left the glass and water jug on his bedside table, next to his glasses, and he drank quickly. The pain through his body had dulled somewhat and he looked down at his skin and found that some of his bruises had turned yellow, while others had disappeared entirely.

He had been out for a couple of days, at least.

It was still painful to move and he gritted his teeth as he slowly swung his legs around and placed his feet upon the ground. He had been clothed in a set of pyjama bottoms, nothing else, and he glanced around the room hoping to find something, _anything_ to wear. His eyes fell on a dressing gown and he pushed his arms through the sleeves and tied the sash around his waist before he moved into the hallway. The floor was freezing against his feet and he shivered, despite the dressing gown, as he walked through the ward. There were people in nearly all the beds; some asleep, others looking blankly ahead. He was reminded of Neville's parents and wondered if these people had been inflicted to something similarly horrific.

He reached the end of the hall and his attention was caught by a girl sitting by a man's bed. The girl who had given him water. She'd fallen asleep at some point but still held the man's hand tightly.

He remembered her words. _"_ _My brother was injured in the battle before last. I've been allowed time from school to see him."_

She looked so much younger, asleep. Almost fragile. He stepped inside her brother's room, wanting to do something, _anything,_ but not knowing what. Eventually, he removed his dressing gown and draped it over her sleeping form. She didn't wake, but snuggled into the warm fabric. He hesitated, his hand still extended, wishing he could do more.

Instead, he left without saying a word.

-o-

The next morning, the dressing gown was back where he'd found it, a note pinned to the front.

 _Thank you._

* * *

 **Author's notes:** A short chapter, but they will get longer as the story continues.

Hope you enjoyed!


	2. Chapter 2

**Chapter 2**

* * *

 **4.**

He was rarely alone.

Morning, noon and night, there was always someone at his bedside, or passing down the hallway.

"It's for your own good," Frances assured him one afternoon, after he shot her a glare when she walked inside, barely an hour since another Healer had 'checked up' on him.

"Really?" Harry asked sarcastically.

"And truly," Frances shot back. "You might believe that you're completely recovered but let me assure you that isn't the case!" Harry looked downward, abashed, but Frances seemed genuinely angry and continued with her tirade. "Those," she snapped, pointing at the stains on the bedsheet. "Do you know where they're from?

Harry shook his head, his head still down.

"This morning, you fell asleep while eating breakfast," she continued. "We took the food and tried to clean the sheet. A quick cleaning charm would have fixed it."

She paused. Harry looked up.

"Another Healer, a trainee, pointed his wand at the sheet to clean up the spill. _You_ went ballistic and struck out, giving him a black eye."

Harry nodded, feeling tremendously guilty. "And the Healer?" he asked softly.

"Is fine," Frances responded. "But has no wish to come anywhere near you again. And one can hardly blame him."

"I suppose not," Harry murmured.

Frances busied herself with potions, which Harry drank without protest; cleaned his sheets and gave him some battered books to keep him occupied.

"You talk a lot," she said suddenly.

"When?"

"While you're asleep," she elaborated.

"What do I say?" Harry asked.

"'Voldemort' mainly," she answered.

Harry almost smiled. He was so accustomed to people's use of 'You-Know-Who' that it was genuinely puzzling to hear see someone say Voldemort's name as if it were nothing. Then again, he reasoned, at this point in time, Voldemort was little more than nothing. Not the most horrific Dark Lord of the ages. Just a school boy.

Harry nodded. "I see."

"What does it mean?"

Harry shrugged a silent 'I don't know', took the final vial of potion, and turned away.

-o-

The girl, to his unknown disappointment, didn't visit him again, though he caught a brief glimpse of her one morning as she trailed sullenly behind a woman that could only be her mother. They shared the same pale skin, and thick, raven-coloured hair; so dark, it almost seemed blue in certain light. Her mother _clicked_ her tongue impatiently as the girl hovered in the ward entrance, clearly not wanting to leave.

"Come _on,_ " the woman hissed, grabbing the girl's wrist to pull her away. "There's nothing more we can do here, and you need to go back to school."

The girl paused for another few moments and her attention was caught by Harry as he shifted in his bed. Her eyes narrowed when they fell on him and, for a second, he thought that she was angry at his silent interruption.

Instead, she granted him a small smile before brushing past her mother without a word.

-o-

 **5.**

"Oh, thank _heavens_ you're back!"

The breath was almost knocked from Minerva's lungs as Pomona Sprout ran headlong into her at the front steps of Hogwarts. The shorter girl gave Minerva a final squeeze before letting go and taking her hand, dragging her inside. Minerva didn't protest as Pomona led her into a disused classroom and sat her down.

"You're not going to believe what has happened since you've been away," Pomona said, anxiously.

"No?" Minerva responded. Her voice was harsher than usual, sarcastic, almost cruel. To her horror, Pomona started crying.

"I'm sorry about Robert, Minerva," Pomona said through her tears. "But… but…"

"But, what?" Minerva asked, already sorry for her tone.

"The Chamber has been opened," Pomona finished.

Minerva's eyes widened. "The Chamber?" she repeated. "As in, the Chamber of _Secrets_?"

Pomona nodded, her bottom lip trembling. "There was a message left…"

 _The Chamber has been opened. Enemies of the Heir. Beware._

"…Beware," Pomona finished.

Minerva blinked; her mind full of a paint-spattered wall.

"Min?"

"What do we have to do?" Minerva said, dismissing her thoughts as she stood up.

"Prefects and teachers have to do patrols," Pomona answered. "We're to use Patronuses to summon others should we need to. Dumbledore's drawn up a roster."

"Good, that's good."

Pomona looked ashamed as she followed Minerva into the hallway. "Min?" she called softly, as Minerva headed toward Gryffindor Tower. How _is_ Robert?"

Minerva paused, closed her eyes for a moment. "Frances said she'll owl me daily."

Pomona nodded, then turned to go to the Hufflepuff common room. Minerva waited until her footsteps had faded before turning and running toward the second floor. Somehow, her feet knew where to take her and she stopped in front of the wall, her eyes wide. The words were huge, terrifying and _somehow_ familiar. As if she had seen them before. A transparency layered over her vision in the form of this same hallway. There were students, _children,_ behind her and they couldn't see this.

"What are you doing here?"

She glanced sideways to find Tom Riddle standing next to her. She couldn't say she was a huge fan of her Slytherin counterpart, but he was polite, which was far more than many of his fellow housemates could claim. Nonetheless, he unnerved her slightly.

"The same as you, I expect," she said, returning her attention to the wall.

"Perhaps."

She ignored him as she gave the wall one final glance-over, before she turned towards the Gryffindor Tower.

"You're pure-blood, aren't you, Minerva?" Tom Riddle called as she neared the corner.

She didn't slow down as she answered. "I don't believe that's any of your business, Tom."

-o-

Minerva went into the Prefect's bathroom that night. She just wanted to be alone, if she were honest with herself. She loved Pomona and Rolanda, she really did, but the constant whispers of 'Slytherin' and 'enemies' grated on her nerves soon enough. She turned on the taps and waited for the bath to fill before she stripped off her clothing and slipped into the water. Contrary to what her animagus form might suggest, Minerva loved water, and she spent several minutes spinning back and forth, to-and-fro until, excess energy dissipated, she floated on her back with her arms outstretched. Her worries about Robert, the Monster, everything seemed to subside as she let herself relax and she felt genuinely better when she finally dragged herself out and wrapped a towel around herself.

There was a vanity in the corner, containing toothbrushes and the like, and she walked through the steam-filled room where her attention was promptly caught by the mirror. She jumped back in fright, and looked both ways, every muscle in her body tense, poised to run.

Written in the glistening condensation on the mirror were the words: _You must not be seen._

Minerva threw caution to the winds and spun around, threw on her dressing gown, and bolted out of the bathroom. She sprinted up the circular staircase, pushing her body as hard as it could, and arrived, out-of-breath, at the portrait of the Fat Lady.

"Not particularly appropriate," the Fat Lady chided.

Minerva rolled her eyes. "Humbug."

The portrait swung open and she kept her head down as she dashed to the girl's dormitories and headed to the sixth-year quarters. It was empty of her classmates and she sat down on the bed, getting her breath back. As her heart-rate slowed down, so did some of her misgivings. It was a prank, she told herself; a horrid prank, but that was all. Now, back in her dormitory, she could see that.

Nodding, she reached out and grabbed her nightgown that she kept beneath her pillow. Her classmates still hadn't returned and she drew the curtains around herself and settled into her bed.

She grabbed her textbook and settled down, wanting to finish the chapter before tomorrow's lesson.

 _You must not be seen._

 _-o-_

 **6.**

Senior Healers at Saint Mungos pressed him for details about _what_ happened to him, but he feigned ignorance.

" _I don't know,"_ he said for the umpteenth time. _"I can't remember."_

Frances gave him a sceptical look, clearly not believing a word, as she checked over his healing injuries. His bruises were nearly all gone, leaving the burns to his back. Usually, such injuries would be easy to heal but these… _time_ injuries could be healed only by that. Time. She placed a hand to his forehead, checking for any sign of a temperature and declared that he would be able to leave sooner rather than later.

"Your sister," Harry said, breaking the silence that had developed. "She told me that her brother was in Saint Mungos. I presume that means he's your brother, too?"

Frances tilted her head slightly to the side, and her lips pursed, displeased her sister had given out such information. "Yes," she answered finally. "Robert. He's an Auror and was injured in a battle with Grindelwald."

Harry nodded. "I'm sorry to hear that."

Frances didn't respond, as if sensing that Harry wished to say more.

"Grindlewald," Harry said softly. "How bad is it?"

Again, Frances didn't speak. Instead, she flicked her wand and a newspaper flew from the outside room and into her out-stretched hand.

"See for yourself."

-o-

Harry read with almost morbid fascination. The headline proclaimed, _'Grindlewald strikes London!'_ and showed the date to be January 21, 1942. He was certainly evil, Harry thought as he turned the pages. This was his third attack on London in the past year and the death toll was huge. At the last battle, he had fought against Dumbledore and it was duel almost to the death, both sustaining injuries that would kill a less-powerful wizard. Harry wondered if Dumbledore had to stay here for any length of time. Or if the Hogwarts Hospital Wing had been sufficient. Then he wondered why he wondered any of this.

Further into the newspaper, Harry saw that the Muggle World War II had overlapped with the wizarding war, and remembered history lessons from his time in Muggle school where the World War was discussed. _Millions killed,_ he remembered reading. _Death tolls unseen before._

Harry threw the newspaper onto the chair in the room in disgust and looked out the window, unsure what on earth he should be doing.

-o-

Harry was discharged the following day and presented with his wand. He felt a surge of relief flood through him, a warmth that spread right through his body as he slipped it into his back pocket.

"Thank you," he said softly.

Frances nodded toward the robes that lay at the end of his bed. "The ones you were found in were unsalvageable," she said gently. "We've brought you these. The bag contains what was in your pockets."

Harry offered a faint smile. "Thank you."

She shook her head, dismissing his thanks. "We're here to help."

-o-

It was cold outside when he left Saint Mungos, after a quick 'goodbye' to Montgomery and Frances. The latter gave him a kiss on his cheek and urged him to 'keep out of trouble.' He merely grinned, not wanting to lie. Harry kept his head down as he wove through the crowded footpath. This world was very different to the one he was used to; both Muggle and wizarding, and he took care to Transfigure his wizarding cloak into a Muggle coat so as not to arouse suspicion. He wandered through the streets of London for some time before deciding to go to one of the few places he knew.

The Leaky Cauldron.

Inside, it was blissfully warm, and he nodded towards the barman - a much-younger Tom - before heading to the small courtyard. A quick tap of his wand and he was inside Diagon Alley which, to his delight, appeared to be much the same. He found his way to a second-hand clothing shop and bought two sets of robes, then ducked into a small coffee shop on the corner. It was fascinating, watching people rush to-and-fro; some towing small children behind them while others held briefcases close to their chest.

A newspaper had been left on the table beside him, and he pulled it across. Grindlewald hadn't struck again, to his relief, though he still took up a large portion of the publication. A small crowd of his followers had been caught and were in Azkaban awaiting trial. He glanced at the names, somehow unsurprised to see 'Black' among the captured.

Sirius had always said his family were a legion of Dark wizards.

Grimacing, he looked up again to find the sky growing dark as the sun fell in the west. It was beautiful to watch, but Harry rose to his feet and headed back to the Leaky Cauldron, hoping he had enough money to rent a room for the night.

-o-

 **7.**

 _The storm was horrific and the wind almost flattened her to the ground. Nonetheless, Minerva pressed forward. She could sense a figure behind her, but that merely spurred her to move faster, push herself harder. Finally, she glimpsed the edge of the cliff and allowed herself a second to glance over the edge. The waves were high, and hurled themselves back against the cliff face. There was absolutely no chance of surviving this fall._

 _It was perfect._

 _Behind her, the pounding footsteps grew closer, but she took a moment to turn her face upward, let the rain pound against her skin._

 _She jumped._

 _Or, rather, she dived. She extended her arms forward, one hand on top of the other, and felt her body cut through the water like a knife. The current captured her immediately, forcing her deeper into the water until she couldn't see the sky anymore; the water was churning far too much. It felt oddly calm, blissful even, and she closed her eyes as she sank still further; made no attempt to try and fight._

 _This had to happen. There was no other choice._

 _A hand grabbed her wrist, their nails digging into her skin, and wrenched her upward._

 _The world turned black._

-o-

Minerva conjured a tiny sphere of light that she put into an old jar and placed it on her bedside table. The faint glow made her feel slightly safer. It was ridiculous, she knew that, only a dream, but she couldn't bring herself to extinguish the tiny flame.

She fell back to sleep with the light still burning.

* * *

 **Author's notes:** So, we're delving a little bit deeper… Wahoo! As I said before, this is a touch confusing but it will make more sense as we go further. 😉 I don't have a beta for this story, and I'm sure some mistakes have fallen through. I apologise.

Hope everybody enjoyed! Please review!


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